The present invention relates to the manufacture of a hollow fiber membrane module having internal sweep generation.
Modules containing hollow fiber membranes have been employed in a wide variety of fluid separation applications. A fluid mixture is brought into contact with one side of the hollow fiber membranes with a pressure differential being maintained across the membrane, whereby the permeable fluid component permeates to the other side of the membrane under a partial pressure gradient. In order to maintain this partial pressure differential across the membrane, a sweep fluid is often employed to help remove the permeating fluid. This is especially important in applications where only small amounts of fluid are to be separated from the fluid mixture, such as in dehydration applications.
U.S. Pat. No. 5,169,412 discloses an integrated system including an air separation membrane system and a membrane dryer. In this system, waste or recycle streams from the air separation membrane are used as purge in the membrane dryer. U.S. Pat. No. 5,205,842 discloses a two-step membrane dryer having a first or "roughing" stage and a second or "polishing" stage. The second stage employs a portion of the dried product gas as a reflux purge to sweep the permeate side of the membrane. European patent application EP 0 702 995 A1 discloses a process and apparatus for separating components of a gas stream, including removing water vapor; i.e., drying, which includes bringing a feed gas into contact with a semi-permeable membrane and maintaining a shallow vacuum on the permeate side of the membrane. Either dry product gas or an external purge stream can be used as the permeate sweep.
U.S. Pat. No. 5,259,869 discloses a process for removing water vapor from a gas stream, wherein a portion of dried product gas is reduced in pressure and returned to the permeate side of the membrane to act as a sweep gas. The dried sweep gas is then captured along with the permeate gas and recycled to the feed system so that none of the dried product gas is lost.
U.S. Pat. No. 4,687,578 discloses a fluid separation module utilizing at least two membrane sections, a sweep generation section and a drying section. Membrane area is minimized and the sweep is generated internally by creating a region where the membrane possesses higher transport flux, preferably near the dry product end, to create a countercurrent flow pattern with respect to the feed. One method used to create the sweep zone is to provide for an uncoated portion of the membrane so as to increase the local membrane flux.
U.S. Pat. No. 5,411,662 discloses a hollow fiber membrane fluid separation device. Tubesheets are provided to encapsulate both ends of the hollow fiber membrane bundle and to separate the feed/non-permeate side from the purge/permeate side of the membrane bundle. At least one of the tubesheets is secured so that the sweep fluid port is in fluid communication with the permeate side of the hollow fiber membrane bundle.
U.S. Pat. No. 5,500,036 describes a process and apparatus for providing an oxygen enriched gas stream. A hollow fiber membrane module is provided wherein one or more of the hollow fibers are shortened so that the feed gas entering those hollow fibers flows onto the permeate side of the fibers in the module thereby providing countercurrent sweep to the permeate side of the hollow fibers. U.S. Pat. No. 5,525,143 discloses a method and apparatus for the dehydration of gases utilizing hollow fiber membranes. The hollow fiber membranes are positioned in a shell and extend from a first tubesheet near the feed gas inlet to a second tubesheet near the product outlet, with each end of the hollow fiber terminating in and penetrating a tubesheet. The second tubesheet has at least one aperture to allow non-permeate gas to return to the permeate side of the fibers to provide a countercurrent sweep.